Zero-Field Overhauser Dynamic Nuclear Polarization

Area of Science:

• Magnetic Resonance
• Physical Chemistry
• Biophysics

Background:

• Overhauser dynamic nuclear polarization (O-DNP) typically requires significant magnetic fields for hyperpolarization.
• Nitroxide radicals are commonly used to induce hyperpolarization in liquids.

Purpose of the Study:

• To demonstrate experimental hyperpolarization of water using O-DNP at effectively zero magnetic field.
• To investigate the efficiency of circularly polarized radiofrequency (RF) fields in O-DNP at low fields.

Main Methods:

• Utilized circularly polarized RF fields generated by orthogonal RF coils to induce selective saturation.
• Employed electron-to-nuclear spectral mapping to record the electron paramagnetic resonance spectrum at 2 nT.
• Compared the efficiency of O-DNP using circularly polarized RF versus linearly polarized RF.

Main Results:

• Achieved hyperpolarization of water via O-DNP at near-zero magnetic field.
• Circumvented the detrimental effects of concurrent positive and negative polarizations using selective saturation.
• Observed a >10³-fold increase in O-DNP efficiency with circularly polarized RF compared to linearly polarized RF.
• Recorded the nitroxide radical's EPR spectrum at a magnetic field as low as 2 nT.

Conclusions:

• Water can be effectively hyperpolarized using O-DNP at near-zero magnetic fields.
• Circularly polarized RF fields significantly enhance O-DNP efficiency at low fields.
• Eliminated the need for auxiliary techniques like sample shuttling or field cycling for low-field O-DNP.